I am having trouble with the following bit of code.
//Send Creation email
ListServDAO.sendCreateEmail(orgId, full, request.getSession().getServletContext());
//Force a 1 minute pause
Timer timer = new Timer();
timer.schedule(new TimerTask() {
public void run() {
//Send add members email
ListServDAO.sendAddMembersEmail(orgId, request.getSession().getServletContext());
}
}, 0, 60 * 1000);
The sendAddMembersEmail function does not wait 1 minute to send after the sendCreateEmail function call. I am not sure why it is not waiting even after reading the java API. I do not wish to use the Thread.sleep method because I want the user to be able to use the application while waiting for the emails to send.
are you intending to repeatedly send emails? if not, why are you using the method which takes 2 longs (i.e. "repeatedly run this task every <period> milliseconds")? use the schedule(task, delay) method (and use a non-zero delay).
2nd parameter is the initial delay which you are passing as 0 hence it it executing it right then and there, pass 60000 second for it to wait for a minute and then send.
Since you just want it to send only once use, call Timer.schedule(TimerTask task, long delay)
Off-topic:
You should consider using ScheduledExecutorService instead of Timer. See Oracle Tutorial.
You have an extra zero.
What you are calling is Delayed with a Fixed-Delay Repeat Execution and what you want is a Single Delay Non Repeat execution.
You have the order of the params wrong:
schedule(TimerTask task, long delay, long period)
Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay.
Swap the 0 and 60*1000.
Related
I was trying some codes to implement a scheduled task and came up with these codes .
import java.util.*;
class Task extends TimerTask {
int count = 1;
// run is a abstract method that defines task performed at scheduled time.
public void run() {
System.out.println(count+" : Mahendra Singh");
count++;
}
}
class TaskScheduling {
public static void main(String[] args) {
Timer timer = new Timer();
// Schedule to run after every 3 second(3000 millisecond)
timer.schedule( new Task(), 3000);
}
}
My output :
1 : Mahendra Singh
I expected the compiler to print a series of Mahendra Singh at periodic interval of 3 s but despite waiting for around 15 minutes, I get only one output...How do I solve this out?
Advantage of ScheduledExecutorService over Timer
I wish to offer you an alternative to Timer using - ScheduledThreadPoolExecutor, an implementation of the ScheduledExecutorService interface. It has some advantages over the Timer class, according to "Java in Concurrency":
A Timer creates only a single thread for executing timer tasks. If a
timer task takes too long to run, the timing accuracy of other
TimerTask can suffer. If a recurring TimerTask is scheduled to run
every 10 ms and another Timer-Task takes 40 ms to run, the recurring
task either (depending on whether it was scheduled at fixed rate or
fixed delay) gets called four times in rapid succession after the
long-running task completes, or "misses" four invocations completely.
Scheduled thread pools address this limitation by letting you provide
multiple threads for executing deferred and periodic tasks.
Another problem with Timer is that it behaves poorly if a TimerTask throws an unchecked exception. Also, called "thread leakage"
The Timer thread doesn't catch the exception, so an unchecked
exception thrown from a TimerTask terminates the timer thread. Timer
also doesn't resurrect the thread in this situation; instead, it
erroneously assumes the entire Timer was cancelled. In this case,
TimerTasks that are already scheduled but not yet executed are never
run, and new tasks cannot be scheduled.
And another recommendation if you need to build your own scheduling service, you may still be able to take advantage of the library by using a DelayQueue, a BlockingQueue implementation that provides the scheduling functionality of ScheduledThreadPoolExecutor. A DelayQueue manages a collection of Delayed objects. A Delayed has a delay time associated with it: DelayQueue lets you take an element only if its delay has expired. Objects are returned from a DelayQueue ordered by the time associated with their delay.
Use timer.scheduleAtFixedRate
public void scheduleAtFixedRate(TimerTask task,
long delay,
long period)
Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals, separated by the specified period.
In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).
Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another.
Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
public void schedule(TimerTask task,long delay)
Schedules the specified task for execution after the specified delay.
you want:
public void schedule(TimerTask task, long delay, long period)
Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals separated by the specified period.
timer.scheduleAtFixedRate( new Task(), 1000,3000);
I use the timer schedule method to send location information to the db every 5 min.
Here is the code:
public void onStart(Intent intent, int startId)
{
this.timer.schedule(new Send(), new Date(), TEN_SECONDS*6*5); //ten_seconds = 10000
}
class Send extends TimerTask
{
public void run()
{
String address = LocationService.this.address;
new SendLocation(LocationService.this.id,address); // a thread that sends the info to the db
LocationService.this.gpsLocation = null;
LocationService.this.networkLocation = null;
}
}
But how come that my db has locations with 7/6 minute diffrence?
The sendLocation checks if the location that i'm going to send to the db is the same as the last one, if true ignore the location else send it.
Which means that the diffrence between each location in my db should be in jump of 5 minute.
Watch this link about Timer schedule Method. It clearly says that :
Schedules the specified task for repeated fixed-delay execution,
beginning at the specified time. Subsequent executions take place at
approximately regular intervals, separated by the specified period.
In fixed-delay execution, each execution is scheduled relative to the
actual execution time of the previous execution. If an execution is
delayed for any reason (such as garbage collection or other background
activity), subsequent executions will be delayed as well. In the long
run, the frequency of execution will generally be slightly lower than
the reciprocal of the specified period (assuming the system clock
underlying Object.wait(long) is accurate).
In your code It might be possible that the run method of Send is taking more than 5 minutes to complete its task because of some heavy task to be performed by SendLocation Thread. So Your db has locations with 7/6 minute difference.
There is no guarantee your TimerTasks will be executed exactly when you request. From the Timer docs --
Each timer has one thread on which tasks are executed sequentially.
When this thread is busy running a task, runnable tasks may be subject
to delays.
and
This class does not offer guarantees about the real-time nature of
task scheduling
Granted, two minutes is a long time, so there might be delays elsewhere.
I was trying some codes to implement a scheduled task and came up with these codes .
import java.util.*;
class Task extends TimerTask {
int count = 1;
// run is a abstract method that defines task performed at scheduled time.
public void run() {
System.out.println(count+" : Mahendra Singh");
count++;
}
}
class TaskScheduling {
public static void main(String[] args) {
Timer timer = new Timer();
// Schedule to run after every 3 second(3000 millisecond)
timer.schedule( new Task(), 3000);
}
}
My output :
1 : Mahendra Singh
I expected the compiler to print a series of Mahendra Singh at periodic interval of 3 s but despite waiting for around 15 minutes, I get only one output...How do I solve this out?
Advantage of ScheduledExecutorService over Timer
I wish to offer you an alternative to Timer using - ScheduledThreadPoolExecutor, an implementation of the ScheduledExecutorService interface. It has some advantages over the Timer class, according to "Java in Concurrency":
A Timer creates only a single thread for executing timer tasks. If a
timer task takes too long to run, the timing accuracy of other
TimerTask can suffer. If a recurring TimerTask is scheduled to run
every 10 ms and another Timer-Task takes 40 ms to run, the recurring
task either (depending on whether it was scheduled at fixed rate or
fixed delay) gets called four times in rapid succession after the
long-running task completes, or "misses" four invocations completely.
Scheduled thread pools address this limitation by letting you provide
multiple threads for executing deferred and periodic tasks.
Another problem with Timer is that it behaves poorly if a TimerTask throws an unchecked exception. Also, called "thread leakage"
The Timer thread doesn't catch the exception, so an unchecked
exception thrown from a TimerTask terminates the timer thread. Timer
also doesn't resurrect the thread in this situation; instead, it
erroneously assumes the entire Timer was cancelled. In this case,
TimerTasks that are already scheduled but not yet executed are never
run, and new tasks cannot be scheduled.
And another recommendation if you need to build your own scheduling service, you may still be able to take advantage of the library by using a DelayQueue, a BlockingQueue implementation that provides the scheduling functionality of ScheduledThreadPoolExecutor. A DelayQueue manages a collection of Delayed objects. A Delayed has a delay time associated with it: DelayQueue lets you take an element only if its delay has expired. Objects are returned from a DelayQueue ordered by the time associated with their delay.
Use timer.scheduleAtFixedRate
public void scheduleAtFixedRate(TimerTask task,
long delay,
long period)
Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals, separated by the specified period.
In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).
Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another.
Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
public void schedule(TimerTask task,long delay)
Schedules the specified task for execution after the specified delay.
you want:
public void schedule(TimerTask task, long delay, long period)
Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals separated by the specified period.
timer.scheduleAtFixedRate( new Task(), 1000,3000);
I was trying some codes to implement a scheduled task and came up with these codes .
import java.util.*;
class Task extends TimerTask {
int count = 1;
// run is a abstract method that defines task performed at scheduled time.
public void run() {
System.out.println(count+" : Mahendra Singh");
count++;
}
}
class TaskScheduling {
public static void main(String[] args) {
Timer timer = new Timer();
// Schedule to run after every 3 second(3000 millisecond)
timer.schedule( new Task(), 3000);
}
}
My output :
1 : Mahendra Singh
I expected the compiler to print a series of Mahendra Singh at periodic interval of 3 s but despite waiting for around 15 minutes, I get only one output...How do I solve this out?
Advantage of ScheduledExecutorService over Timer
I wish to offer you an alternative to Timer using - ScheduledThreadPoolExecutor, an implementation of the ScheduledExecutorService interface. It has some advantages over the Timer class, according to "Java in Concurrency":
A Timer creates only a single thread for executing timer tasks. If a
timer task takes too long to run, the timing accuracy of other
TimerTask can suffer. If a recurring TimerTask is scheduled to run
every 10 ms and another Timer-Task takes 40 ms to run, the recurring
task either (depending on whether it was scheduled at fixed rate or
fixed delay) gets called four times in rapid succession after the
long-running task completes, or "misses" four invocations completely.
Scheduled thread pools address this limitation by letting you provide
multiple threads for executing deferred and periodic tasks.
Another problem with Timer is that it behaves poorly if a TimerTask throws an unchecked exception. Also, called "thread leakage"
The Timer thread doesn't catch the exception, so an unchecked
exception thrown from a TimerTask terminates the timer thread. Timer
also doesn't resurrect the thread in this situation; instead, it
erroneously assumes the entire Timer was cancelled. In this case,
TimerTasks that are already scheduled but not yet executed are never
run, and new tasks cannot be scheduled.
And another recommendation if you need to build your own scheduling service, you may still be able to take advantage of the library by using a DelayQueue, a BlockingQueue implementation that provides the scheduling functionality of ScheduledThreadPoolExecutor. A DelayQueue manages a collection of Delayed objects. A Delayed has a delay time associated with it: DelayQueue lets you take an element only if its delay has expired. Objects are returned from a DelayQueue ordered by the time associated with their delay.
Use timer.scheduleAtFixedRate
public void scheduleAtFixedRate(TimerTask task,
long delay,
long period)
Schedules the specified task for repeated fixed-rate execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals, separated by the specified period.
In fixed-rate execution, each execution is scheduled relative to the scheduled execution time of the initial execution. If an execution is delayed for any reason (such as garbage collection or other background activity), two or more executions will occur in rapid succession to "catch up." In the long run, the frequency of execution will be exactly the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).
Fixed-rate execution is appropriate for recurring activities that are sensitive to absolute time, such as ringing a chime every hour on the hour, or running scheduled maintenance every day at a particular time. It is also appropriate for recurring activities where the total time to perform a fixed number of executions is important, such as a countdown timer that ticks once every second for ten seconds. Finally, fixed-rate execution is appropriate for scheduling multiple repeating timer tasks that must remain synchronized with respect to one another.
Parameters:
task - task to be scheduled.
delay - delay in milliseconds before task is to be executed.
period - time in milliseconds between successive task executions.
Throws:
IllegalArgumentException - if delay is negative, or delay + System.currentTimeMillis() is negative.
IllegalStateException - if task was already scheduled or cancelled, timer was cancelled, or timer thread terminated.
public void schedule(TimerTask task,long delay)
Schedules the specified task for execution after the specified delay.
you want:
public void schedule(TimerTask task, long delay, long period)
Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay. Subsequent executions take place at approximately regular intervals separated by the specified period.
timer.scheduleAtFixedRate( new Task(), 1000,3000);
How do you activate or run a loop every tenth of a second? I want to run some script after an amount of time has passed.
Run a script every second or something like that. (notice the bolded font on every)
You can use a TimerTask. e.g.
timer = new Timer();
timer.schedule(new RemindTask(), seconds*1000);
You simply need to define a Runnable. You don't have to worry about defining/scheduling threads etc. See the Timer Javadoc for more info/options (and Quartz if you want much more complexity and flexibility)
Since Java 1.5:
ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
executor.scheduleAtFixedRate(new RepeatedTask(), 0, 100, TimeUnit.MILLISECONDS);
and
private class RepeatedTask implements Runnable {
#Override
public void run() {
// do something here
}
}
(remember to shotdown() your executor when finished)
You sleep.
Check out Thread.sleep() but be warned that you probably really don't want your whole program to sleep, so you might wish to create a thread to explicitly contain the loop and it's sleeping behavior.
Note that sleep only delays for a number of milliseconds; and, that number is not a perfect guarantee. If you need better time resolution you will have to use System.currentTimeMillis() and do the "time math" yourself. The most typical scenario is when you run something and you want it to run ever minute. The time the script runs must be captured by grabbing System.currentTimeMillis() before and after the script, and then you would need to sleep the remaining 1000 - scriptRunTime milliseconds.